Over the past decades, there have been a significant number of terrorist attacks on government buildings owned by the United States and other countries both outside of the United States and within. For example, in 1993, terrorists exploded a car bomb inside the garage of the World Trade Center located in New York City, resulting in loss of life and significant property damage. Since then, in 1995, other extremists exploded a truck outside of the Federal Building located in Oklahoma City, Okla. also resulting in significant loss of life and property damage. In 1998, the United States embassies in Nairobi and Dar Es Salaam were also subject to terrorist attacks by car bombs, each of which resulted in significant loss of life and property damages. More recently, the tragic events at the World Trade Center in New York City and the Pentagon in Virginia has further emphasized the long felt need to develop and manufacture building materials which are able to withstand the shock wave from car bomb explosions and other similar terrorist attacks.
Traditionally, the support structures for many buildings are made from reinforced concrete. In some instances, when stronger materials are desired, prestressed concrete has been used. For example, prestressed concrete has been used in buildings, underground structures, TV towers, floating storage and offshore structures, power stations, nuclear reactor vessels and numerous types of bridge systems including segmental and cable-stayed bridges. Prestressed concrete has been considered advantageous over reinforced concrete in instances where a shallower depth for the same span and loading conditions is desired. Prestressed concrete has also been considered advantageous over reinforced concrete where a lighter weight material is desired. Prestressed concrete also requires less concrete and less reinforcement due to its added strength. Unfortunately, prestressing operations themselves results in added costs: formwork is more complex, since the geometry of prestressed sections is usually composed of flanged sections with thin webs. Thus, it would be desirable to have a building material which obtains the added strength of prestressed concrete, but were to weigh less and thus require less support structure. Lighter support structures have the ability to increase useable space within the same footprint, and/or increase the number of floors that can be supported, and/or withstand greater impact forces, such as caused by earthquakes. Typically, prestressed concrete will contain water, either as a result of its manufacturing process or due to water migrating from outside the concrete. As a result of the presence of such water, the tension members that prestress the concrete, usually made of steel or other corrosive metals, may rust and thus weaken the structure. Further, as a result of the presence of such water, when the prestressed concrete is exposed to typical heat/thaw cycles it can crack. Also, as a result of the presence of such water, in the case of fire, the prestressed concrete is subject to failure as a result of steam formation. Another drawback to using prestressed concrete is that it has a limited variety of aesthetic appearances.
While the concept of using foam glass as a construction material is well known in the prior art, generally such foam glass has been used as a high temperature insulator and thus seeks to minimize its density and weight and is not suitable for absorbing sufficient energy from a shock wave from unexpected explosions or to resist an earthquake and/or wind and heat loading. The shortcomings in such conventional foam glass as relevant to this long standing problem are now described.
For example, Pittsburgh Corning Corporation (“PCC”) of Pittsburgh, Pa. has developed and marketed a product known as Foam Glas® Insulation Systems, which is described in U.S. Pat. Nos. 3,959,541, 4,119,422, 4,198,224, 4,571,321 and 4,623,585. Because the focus of these developments are directed to making a foam insulating material, the Foam Glas® Insulation Systems tile commercially sold by PCC is relatively light, weighing 9.5 lb./cu. ft. Furthermore, since the purpose of this tile is to be used as thermal insulation, it lacks surface strength, and can be dented very easily. Because the Foam Glas® Insulation Systems tile is of relatively low density, e.g., 9.5 lb./cu. ft., such tiles will easily break when exposed to forces typically exerted on exterior walls of a building or other structure. Thus, such tiles are not suitable to be used as tiling for an exterior wall. Similarly, this foam, when exposed to a shock wave from an explosion will absorb very little of the shock waves energy when it implodes. A shock wave is a measure associated with explosions which is easily understood by those skilled in the art as being a pressure front resulting from an explosion.
Others have also attempted to use foam glass tiles as the outer skin-surface of buildings. For example, U.S. Pat. No. 5,069,960 discloses a thermally insulating foam glass tile that is coated with an outside surface to make a hard skin to protect the outside of a building. The tiles disclosed are fabricated in extremely small sizes, i.e., 18 cm×18 cm×6 cm, and the interior foam material which makes up the bulk of the material is generally of a low density. Significantly, there is no indication that the strength of the material disclosed is capable of absorbing sufficient energy from an explosion, and indeed the size of the disclosed tiles would not be ideally suitable for absorbing such energy. Furthermore, there is no indication that small size pores are being used.
Prior work by the inventors and others have developed methods for making foam glass tiles of a wide a variety of densities as described in U.S. Pat. No. 4,430,108 that can be used for building materials. While the techniques and methods disclosed were useful to manufacture then-standard size tiles of 4.25 in.×4.25 in.×0.25 in., this disclosure does not teach how to manufacture tiles of a larger size, for example 2 ft.×2 ft.×3 in. Likewise the tiles manufactured under these methods were relatively light, e.g., less than 10 lbs., and were not manufactured to withstand the effects of an explosion. To the contrary, these methods sought to optimize the thermal insulation properties of the material, and thus made smaller, lighter and weaker tiles.
While still others have worked on trying to make some large-size porous shaped bodies, these have been smaller in critical dimensions and of lower density than the present invention and not suitable to absorb a substantial amount of a shock wave which impacts the bodies associated with an explosion or earthquake. For example, U.S. Pat. No. 5,151,228 describes a process for manufacturing large-size porous shaped bodies of low density by swelling, in order to manufacture large-size cellular ceramic structural elements, e.g., multi-story high wall elements having a low weight. In the example, it discloses a tile 8.2 ft.×1.64 ft.×2 in., with a density of 26 lb./cu. ft. and a mass of 60 lbs. It also teaches to obtain a low density in order to optimize thermal insulation. Thus, this foam when exposed to a shock wave from an explosion or earthquake or heat or wind loading or stress of any kind will absorb very little of the shock waves energy when it implodes.
Further, others, such as Central Glass Co. Ltd., of Ube, Japan, have attempted to make foam glass using densities in the range of 0.3 to 0.6 g/cu. cm (or 18.7 to 37.4 lb./cu. ft.) as disclosed in U.S. Pat. No. 4,798,758. The '758 patent explains that in order to make the foam glass stronger, an outer layer is also added which has a density in the range of 0.8 to 1.7 g/cu. cm and a thickness of 1.5 to 20 mm. In the examples shown, all the samples which are over 30 lbs. in weight were found to be unacceptable from a cutability and impact resistance perspective, for among other reasons that the surface had appreciable breaking and sometimes cracking, thus not providing a closed pore surface. Further, U.S. Pat. No. 4,833,015, a later patent by Central Glass Co. Ltd., explains the tensile strength perpendicular to the surface of the tile described in the '758 patent was very poor, i.e., below 150 lb./sq. in., thus making it unsuitable for purposes of the present invention. Even after putting a third layer to improve the strength of the product as described in the '015 patent, the best tensile strength achieved was below 200 lb./sq. in., and making it unsuitable for purposes of the present invention.
Other efforts by Central Glass Co., Ltd. attempt to make higher density glass tiles, such as U.S. Pat. No. 4,992,321. However, these tiles do not appear to be a closed pore structure and there is no indication as to their strength. Indeed, filler materials are used in an attempt to increase the strength with no reporting data. Further, the tiles disclosed were also very thin, 33 mm (or 1.3 in.).
Still others have attempted to make foam glass tiles with smaller pore size. For example, in U.S. Pat. No. 5,516,351, the relationship of pore size to thermal resistivity is shown in which the best pore size is always greater than 1.0 mm. Similarly, the density is always less than 12 lb./cu. ft. Other efforts to use small pore size and larger densities, such as U.S. Pat. Nos. 3,951,632 and 4,758,538, failed to achieve comparable strengths and does not disclose achieving a closed pore outer skin as disclosed by the present invention.
In the past, although some have made tempered glass, such as used in windshields, no one has successfully made prestressed foam glass tiles, like the present invention. Similarly, while it has been suggested in U.S. Pat. No. 4,024,309, to prestress foam glass slabs, the methods disclosed to achieve such prestressing are inoperable. Specifically, the '309 patent discloses a process whereby outer metal sheets are to be placed in tension by stretching while foam glass is formed therebetween. Unfortunately, the temperatures at which such foam glass is formed will cause the outer metal sheets which are in contact therewith to stretch and thereby releasing the intended tension. As such, the process disclosed would be inoperable. Further, the method disclosed in the '309 patent utilizes water cooling of the foam glass, which will cause the outer edge to go through the glass transition before the interior portion, thus causing the interior portion to shrink due to the higher thermal expansion coefficient of the liquid center as compared to the solid exterior, which will cause the final product to be in tension in the center rather than in compression as desired. Thus, even if the resulting product does not break from such tensions, the desired prestressing would be the opposite as desired, making the final product very weak at best.
Unlike the prior art discussed above, the tiles of the present invention are designed and constructed of various materials so that such tiles have properties which are ideal for withstanding the shock wave associated with large explosions or make a building or other structure resistant to earthquakes and other shock waves.
Thus, while the prior art is of interest, the known methods and apparatus of the prior art present several limitations which the present invention seeks to overcome. In particular, it is an object of the present invention to provide a prestressed, strong foam glass tile which can be used as a building material or otherwise.
It is another object of the present invention to provide a prestressed, strong foam glass tile that is lighter than prestressed concrete.
It is another object of the present invention to provide a prestressed, strong foam glass tile that is stronger than prestressed concrete.
It is a further object of the present invention to provide a prestressed, strong foam glass tile that can withstand higher temperatures than prestressed concrete.
It is a further object of the present invention to provide a prestressed, strong foam glass tile that allows substantially less water penetration than prestressed concrete, so as to protect the support members and to prevent cracking due to freeze/thaw cycles, and to prevent steam explosions inside the concrete in case of fire.
It is a further object of the present invention to provide a prestressed, strong foam glass tile which can be used on the critical surfaces of buildings at high risk for terrorist attacks, in combination with cement, steel or other building materials.
It is a further object of the present invention to provide a prestressed, strong foam glass tile which can come in a variety of aesthetic appearances.
These and other objects will become apparent from the foregoing description.